1. Field of the Invention
The present invention relates to a liquid crystal display device, and particularly, to a liquid crystal display device which improves the efficiency of a glass substrate by integrating shorting bars and thereby minimizing a margin of the liquid crystal panel formed on the glass substrate.
2. Description of the Background Art
A liquid crystal display (LCD) device is a transmittive flat panel display device, and is used in various electric devices such as mobile phones, PDAs and notebook computers. The LCD can be formed as a small, lightweight and power-efficient device, and can realize a high image quality. Therefore, the LCD has been researched and developed more than any other display devices. Moreover, as needs for digital TVs, high image quality TVs and wall mounted TVs increase, the LCD with a larger display area, which can be used in these TVs, is being researched actively.
Generally, LCDs can be divided into a few kinds according to the methods of operating liquid crystal molecules. However, an active matrix thin film transistor LCD is mainly used presently due to its rapid reaction speed and a minimal production of residual images.
FIG. 1 shows a structure of a general liquid crystal panel 1 in the above discussed TFT LCD. As shown therein, the liquid crystal panel 1 of the TFT LCD comprises a displaying unit 2 on which an image is realized. A plurality of gate lines 3 and data lines 5 defining a plurality of pixel areas are disposed in longitudinal and transverse directions on the displaying unit 2. A thin film transistor (TFT) 7, which is a switching device, is disposed in each of the pixel areas. Each TFT 7 is switched when a scan signal is input through the corresponding gate line 3 to pass a signal from the corresponding data line to the corresponding pixel electrode 9. Also, gate pads 12 and data pads 14 are formed on the ends of the gate lines 3 and data lines 5. Although it is not shown in FIG. 1, a gate driving IC and a data driving IC are mounted on the outer portions of the liquid crystal panel 1 to supply signals to the gate lines 3 and to the data lines 5 through the corresponding gate pads 12 and data pads 14.
Although it is not shown in FIG. 1 in detail, each thin film transistor 7 includes a gate electrode to which a scan signal is applied from the gate driving IC, and being connected to the corresponding gate line 3; a gate insulating layer formed on the gate electrode; a semiconductor layer formed on the gate insulating layer for forming a channel layer as the scan signal is applied to the gate electrode; and source/drain electrodes formed on the semiconductor layer for applying a signal to the pixel electrode 9. This signal is input through the corresponding data line 5 from the data driving IC as the channel layer is formed.
Generally, the liquid crystal panel includes an upper substrate and a lower substrate. The components described above, such as the gate lines, the data lines, the thin film transistors and pixel electrodes, are all formed on the lower substrate. A color filter for realizing colors is formed on the upper substrate. The upper substrate and the lower substrate are attached and a liquid crystal is injected therebetween to complete the liquid crystal display device.
In the structure of the LCD device constructed as above, the thin film transistor is a basic component for driving the LCD device. Therefore, after the thin film transistors are formed on the lower substrate, an inspection for identifying whether or not the thin film transistors are operated normally should be performed.
In order to inspect the operation of each thin film transistor, a test signal is applied to the corresponding gate electrode and to the corresponding source/drain electrodes, and then the voltage on the corresponding pixel electrode is measured. If there is a voltage change in the pixel electrode, it means that the test signal input through the source/drain electrodes was successfully applied to the pixel electrode and the thin film transistor is operating normally. If there is no voltage change in the pixel electrode, it indicates that an error or defect exists in the thin film transistor.
Generally, the test signal is input through the gate pad 12 and the data pad 14 formed on the ends of the gate line 3 and the data line 5. An additional wiring is needed to input the test signal.
Reference numerals 16 (16a, 16b) and 18 (18a, 18b) shown in FIG. 1 represent bars provided for inspecting the thin film transistors. These bars are also called as ‘shorting bars’. These shorting bars 16 and 18 are formed on an outer portion of the displaying unit 2 in the liquid crystal panel 1, where this outer portion of the displaying unit 2 is generally called as a ‘dummy region’.
As shown in FIG. 1, the shoring bars 16 and 18 formed in the dummy region can be divided into gate shorting bars 18a and 18b and data shorting bars 16a and 16b. The respective shoring bars are formed in pairs to be connected to respective odd gate pads 12 and odd data pads 14 and to be connected to respective even gate pads 12 and even data pads 14.
Also, the shorting bars 18a and 18b for the gates are connected to a gate test signal generating unit 20 to supply the gate test signals output from the gate test signal generating unit 20 to the gate lines 3. The shorting bars 16a and 16b for the data lines are connected to a data test signal generating unit 22 to supply the data test signals output from the data test signal generating unit 22 to the data lines 5.
Generally, a plurality of liquid crystal panels are fabricated altogether. That is, a plurality of liquid crystal panels are first fabricated on a single glass substrate of a large area. Then, this glass substrate is processed and cut into multiple sections to produce multiple liquid crystal panels. Therefore, the yield of an LCD device is dependent on how many liquid crystal panels can be fabricated on a single glass substrate (that is, how efficiently the glass substrate is used).
FIG. 2 shows an example of a glass substrate 30 on which a plurality of liquid crystal panels (for example, 6 panels) are formed. As shown therein, six liquid crystal panels 1 are provided. Each liquid crystal panel 1 comprises a displaying unit 2 on which an image is realized and a dummy region 4 in which the shorting bars 16 and 18 are formed. In this environment, it is difficult to reduce the size of the displaying unit 2 having a fixed number of pixels since it requires fine pitch technology.
Therefore, in order to improve the efficiency of the glass substrate, it is desirable that the size of the dummy regions 4 of the liquid crystal panels 1 is reduced. However, in the general LCD device, since the gate shorting bars 18a and 18b and the data shorting bars 16a and 16b are formed in pairs, it is very difficult to reduce the size of the dummy regions (that is, the margin of the liquid crystal panel).